Hello

Sorry for the long delay
In the process of moving house.

I have attached 3 graphs from o2 sensors

2 look normal but one is below the range you have suggested it should be.

Just to tell you I am in the UK and have a RHD UK supplied Blazer.

I have noticed the sensors are 1, 3 and 5 on the Torque app.

I assume this o2 reading is post cat? And is nirmal

This o2 reading seems in range?

This one is not the normal o2 reading?

 

There can be confusion on the O2 sensor labeling in some OBDII apps. The formal labels for your 98 are:

1. Driver upstream B1S1
2. Pass upstream B2S1
3. Post cat B1S3 (this is B1S2 for other model years

I am not familiar with your RHD UK supplied Blazer so I don't know if that affects this. Your first graph would be normal for a new post cat (roughly flat line somewhere between 0.45 and 0.7v) but that graph is suspiciously perfect and so it might be the default presented if the sensor mapping is wrong. 0.45v is the bias voltage presented to all sensors by the ECM.

Your second graph is good, thats what a precat sensor should look like

Your third graph if accurate is not normal.

I would want to verify that your sensor mapping/graphing is accurate, Les might be able to help here, he knows more about these apps than I do. We could also verify at the sensors/app with some experiments if needed.

George

 

Checked all 3 sensors yesterday with a multimeter and the suspect o2 sensor (your drivers side) has no voltage where the other two do.
Now just to get the thing off and put a new one in. Very little room for a socket and rachet so I may cut off the top part so I can get a good grip on it.

 

If you have a bad O2 sensor circuit it can be:

1. The sensor
2. The wiring (heater power and 0.45 bias voltage)
3. The ECM (rare)

There is an O2 sensor wrench:



George

 

I use this one:




George

 

I tested the two wires of the same colour which all 3 sensores had voltage for the heater.
It was the other two wires I tested which the suspect bad o2 sensor didn't show any life but the other two flutuated as you had suggested they would.
Hopefully this will solve the rough idle.
Will post back when I have changed the sensor.
Really appreciate your help!

 

Hello.... Back again, changed the o2 sensor yesterday that was bad. Hoped that would solve my issue but hasnt.
On the live data the new o2 sensor is now functioning as should.

When the engine runs at idle its still sounds like a missfire or surges.
Acceleration its sounds the same.
Will check sparks plugs are not sooty
Running rich
Smoky tailpipe and sooty with condensation drips from it too.
Regards John

 

1) An engine running rich can kill O2 sensors so its best to analyze and get to the bottom of the root cause. What are your 4 fuel trims at idle and again at 2500 rpm's?

2) Have you done a fuel pressure leak down test?

3) Do all 3 O2 sensors now look normal on a live graph.

George

 

Previously done fuel pressure leakdown test
All o2 sensors are in range

Spark plugs clean and not sooty.

I will look at fuel trims next

 

These are a screenshot of the fuel trims